Frictionless and low-friction bearings are useful in a variety of mechanical instruments, including actuators for the movement of magnetic recording heads in computer disk file systems. Pneumatic bearings are useful for supporting loads with low friction. While some pneumatic bearings are supplied with an external source of air under pressure to separate the bearing surfaces for purposes of pneumatic lubrication, it is possible with a pneumatodynamic bearing with a built-in transducer to generate air pressure in the bearing. One form of pneumatodynamic bearing is shown as a squeeze bearing, from the work of E. O. Salbu "Compressible Squeeze Films and Squeeze Bearings", Trans. ASME Journal of Basic Engineering, June 1964. A pumping action is caused by high frequency oscillations of a disk-shaped bearing which occurs at such a high frequency that the gas cannot flow out of the bearing space fast enough to avoid compression. It is also referred to as pumping action attributable to compression occurring in the compressible gas film.
U.S. Pat. No. 3,339,421 for a "Dynamic Gas Film Supported Inertial Instrument" describes a cylindrical PZT piezoelectric cylinder providing pulsations of the entire cylinder to provide a gaseous squeeze bearing about the periphery of the cylinder and on its axial ends in a gyroscopic mounting.
Copending and commonly assigned U.S. patent application Ser. No. 273,280 filed June 12, 1981 for "Planar and Cylindrical Oscillating Pneumatodynamic Bearings" of Scranton describes a pneumatodynamic bearing in cylindrical form with an inner tubular portion of molybdenum and an outer tubular layer of piezoelectric material. The bearing flexes and unflexes at the frequency of excitation applied to the bearing. The bearing is mounted at a mechanical node of its vibration. This form of mounting is intended to reduce the vibration which is passed on to the load which can be a magnetic recording head which is to be positioned accurately with respect to a magnetic recording medium upon which data is stored with great density. Accordingly, to locate the magnetic recording head in its correct position accurately and quickly, vibration must be minimized.
Tubular squeeze bearings nominally provide constraint against four degrees of freedom, two of which are freedom of rotation and two of which are freedom of translation. These four constraints leave the shaft of the bearing free to rotate (roll) about its axis and to translate along the length of its axis.
It has been found by experimentation that optimum constraint against pitch and yaw requires further improvements for linear actuator applications such as for actuators for magnetic recording disks.
A linear tubular bearing comprises a tubular member and a rod which supports the tubular member slideable along the length of the rod. The tubular member comprises a transducer composed of two colinear tubes, of sufficient length to afford some improvement in the constraint against pitch and yaw rotation. The tubes are shown to be cylindrical.